1. Field of the Invention
The present invention relates to an engine structure of a snowmobile.
2. Related Art
Snowmobiles have been mainly equipped with two-stroke-cycle engines because of requirements of their light weight and high power. However, in view of environmental matters, there is a recent tendency or requirement for a snowmobile to be mounted with a four-stroke-cycle engine.
The four-stroke-cycle engine, such as shown in Japanese Patent Laid-open Publication No. 2001-214750, has an overall height higher than that of the two-stroke-cycle engine and is equipped with a turbo-charger and an inter-cooler so as to have the same power even with the same size as the two-stroke-cycle engine.
However, an engine room of the snowmobile is located at a position in front of a steering bar covered with an engine hood, and the engine hood has a shape inclined forward downward with the highest position being disposed at the lowermost position of a headlight so as not to intercept an optical axis of the headlight. Thus, according to such arrangement, it is difficult to lay out the four-stroke-cycle engine and auxiliary machinery such as turbo-charger in the snowmobile.
Furthermore, inside the engine hood, ambient air temperature is increased by heat generated through the engine operation and the intake air temperature is also increased, which will result in the lowering of an output efficiency of the engine, as well as generating an adverse affect on the equipment or elements disposed inside the engine.